What happens to signals higher in frequency than the critical frequency?

What causes the maximum usable frequency to vary?

What does maximum usable frequency mean?

What can be done at an amateur station to continue HF communications during a sudden ionospheric disturbance?

What is one way to determine if the maximum usable frequency (MUF) is high enough to support 28 MHz propagation between your station and western Europe?

What usually happens to radio waves with frequencies below the maximum usable frequency (MUF) when they are sent into the ionosphere?

At what point in the solar cycle does the 20-metre band usually support worldwide propagation during daylight hours?

If we transmit a signal, the frequency of which is so high we no longer receive a reflection from the ionosphere, the signal frequency is above the:

Communication on the 80 metre band is generally most difficult during:

The optimum working frequency provides the best long range HF communication. Compared with the maximum usable frequency (MUF), it is usually:

During summer daytime, which bands are the most difficult for communications beyond ground wave?